Building materials using natural lumbers have a problem in that the original shape or texture of the building materials is easily damaged due to water or sunlight. For this reason, much research has been carried out to develop a wood plastic composite lumber that can eliminate the problem of the natural lumbers. The wood plastic composite lumber is manufactured by mixing granular or pellet-shaped wood fiber and synthetic resin at a predetermined mixing ratio, adding various additives according to the use of products, and forming the mixture into the shape of a panel using extrusion or injection.
In the wood plastic composite panel manufactured as described above, however, the synthetic resin, which is a matrix component of the resin composite, constitutes an outer layer on the surface of the panel after the extrusion. As a result, the appearance and texture peculiar to the natural lumbers are not provided due to the oil-like tactile sensation and high gloss peculiar to the plastic although the wood fibers are used as a filler. Consequently, various attempts have been made to solve the problems of the wood plastic composite panel.
Specifically, several attempts have been made to provide the inherent appearance or surface texture of the natural lumbers to the wood plastic composite panel. For example, a method of performing extrusion using pigment having different colors, a method of manually processing a wood pattern, a method of transferring or printing a wood pattern, and a method of laminating films having a wood pattern of natural lumbers or artificial materials have been usually used. However, these methods generally have problems in that the manufacturing process is very complicated, and, in some cases, the durability of products is lowered.
In order to solve the above-mentioned problems, there has been proposed a method of forming an embossed structure on the surface of the wood plastic composite panel so as to directly provide a wood pattern to the surface of the wood plastic composite panel. This method omits the aforesaid post-processing operation, and therefore, it is possible to manufacture a wood plastic composite panel having high durability with the reduction of manufacturing costs. Although the wood plastic composite panel manufactured by this method exhibits wood pattern maximally similar to the cut-open surface of the natural lumber, the wood plastic composite panel has high gloss, and, when a user touches the wood plastic composite panel, oil-like tactile sensation peculiar to the synthetic resin is felt by the user. As a result, the provision of luxury appearance and texture of the natural lumber is limited although the provision of the wood pattern is possible.
There has been also proposed a method of using large-sized wood fiber having a size of approximately 40 to 60 meshes as a filler so as to increase the percentage of the wood fiber directly exposed to the surface of the panel, and thus, to provide the texture of the natural lumber. However, the coupling force of the wood fiber is decreased with the increase in size of the wood fiber, and therefore, the strength of the panel is lowered. Also, the wood fiber is irregularly exposed to the surface of the panel, and therefore, the tactile sensation is decreased.
In the case of a natural lumber panel manufactured by directly processing a natural lumber, the natural lumber panel exhibits excellent appearance and texture after the surface of the manufactured natural lumber panel is smoothly processed. Consequently, a high-quality natural lumber panel, the surface of which has been sophisticatedly treated, is usually used for interior and exterior decorations of buildings. The surface-treated natural lumber panel has a beautiful wood pattern, a smooth and soft tactile sensation, and appropriate gloss. As a result, it is possible to ideally represent the wood pattern. This is accomplished by the unique physical properties of a cellulose polymer constituting the lumber and complex actions of the natural lumber tissues.
When the surface of a wood plastic composite lumber is smoothly treated in the same manner as the natural lumber, on the other hand, the wood plastic composite lumber exhibits high gloss and oil-like tactile sensation peculiar to the synthetic resin. Consequently, there is very high necessity of a technology for providing the appearance and texture similar to the cut-open surface of a natural lumber with the reduction of manufacturing costs although a resin composite including synthetic resin and wood fiber is used as a material.